The present invention relates generally to hand tools having a mechanism to withdraw the strap of a cable tie away from the head of the cable tie to tension the cable tie around an object and to sever the strap adjacent the head of the cable tie when a predetermined tension is reached in the cable tie. Specifically the present invention relates to a cable tie tensioning and severing tool that is specially designed to reliably and repeatedly sever the straps of cable ties that have been stretched to longitudinally orient the nylon strap material.
Prior tools of a design similar to the present invention are illustrated by U.S. Pat. Nos. 3,661,187 and 3,830,263. These tools were designed for the application of molded nylon cable ties that were not stretched to orient the plastic straps of the ties.
The tool of U.S. Pat. No. 3,661,187 severed the strap of a cable tie by selectively pivoting a linkage to force a blade through the thickness of the tie strap and just prior to the complete severance of the strap releasing the force applied to the blade to withdraw the blade. The blade of the tool notches the strap allowing the relatively soft strap to yield under the tensioning force applied by the tool to completely sever the strap.
The tool of U.S. Pat. No. 3,830,263 severed the strap of a cable tie by selectively driving a cutting blade through the strap of a cable tie against an anvil.
A commercial tool with a mechanism similar to the mechanism of U.S. Pat. No. 3,661,187 utilizes an elastomeric cord blade stop disposed in the path of a cutting blade such that after the blade has severed the strap the blade engages the elastomeric cord to prevent further translation of the blade into engagement with a metal surface of the tool.
A commercially desirable cable tie application tool must be able to tension and cleanly sever thousands of cable tie straps before replacement of its severance blade is necessary. The use of prior tools to tension and sever stretch oriented cable ties has not proven satisfactory. Stretch oriented cable ties are produced by heating the strap of each molded nylon cable tie and stretching the strap to increase its length and decrease its cross sectional area. The stretching of the strap of the tie results in a tough, hard and relatively more brittle cable tie strap that requires increased force to sever the strap.
The use of a tool that does not completely sever the stretched strap while supporting it against an anvil has been found to result in a brittle fraying of the stretched strap of the tie leaving an unacceptable jagged sharp edge to the severed strap. Also the severance blade of prior anvil tools, when driven by the higher force necessary to sever a stretched strap, is quickly dulled by repeated contact with the hard metal anvil of prior tools.